1. Field of the Invention
The present invention relates to a sensor for detecting for condensation on a window, especially a vehicle window, and the use thereof in a sensor module.
2. Description of the Background Art
As is known in the conventional art, the influencing variables most important for a sense of comfort are considered during regulation in controlled heating and air conditioning units. Incipient condensation on the windshield or other windows, in particular, is to be prevented thereby. Condensation occurs when at a given relative humidity in the vehicle through external effects the window temperature is or becomes colder than the air temperature in the interior, and thus the temperature on the interior side of the window falls below the dew point. An increase in interior humidity also raises the risk of condensation formation. Condensation or moisture sensors are used for detection.
A device for detecting the degree of dew formation or icing of a vehicle window is disclosed in DE 43 16 557 A1. A small-scale sensor provides a signal about the degree of the dew formation or icing of a large window pane area. In this case, the sensor is connected with the vehicle window in a heat-conducting manner, which is performed by gluing the sensor to the vehicle window. The sensor itself is connected to an evaluation unit via external lines. Based on the information from the evaluation unit, countermeasures, e.g., turning on of a fan motor, are activated at a proper time.
DE 695 04 803 T2 discloses a device for defogging vehicle windows. A combined temperature sensing element and moisture sensor are glued onto the windshield.
A generic capacitive moisture sensor for air conditioning units is presented in an article in ATZ Automobiltechnische Zeitschrift 102 (2000)1 on pages 42-44, in regard to both structure and function. The capacitive moisture sensor is housed in a module, which has a thermopile for measuring the window temperature. The relative humidity is determined with use of the described capacitive thin-layer sensor. This sensor at a predefined temperature, provides the ratio of the existing humidity and the maximum possible humidity. When the maximum possible humidity is reached, the corresponding temperature is described as the dew point. If the dew point on the windshield apron is calculated by using the measured relative humidity and temperature, then if the window surface temperature is known, the difference of the two signals will provide a value as an indicator for condensation formation.
It is therefore an object of the present invention to describe a sensor for detecting wetting or incipient condensation on the surface of a window.
The invention is based on the idea of bringing a sensor directly to the window temperature, so that an otherwise necessary determination of the window temperature is not required, because the sensor assumes the temperature of the window and thus a tendency for condensation can be determined immediately. Only the relative moisture on the window is measured, whereby the thus measured window moisture represents a direct indication for the tendency for condensation. Through the direct thermal coupling of the sensor to the window, the sensor exhibits virtually no time delay for detection.
The direct thermal coupling occurs preferably via a metal plate, which simultaneously forms the bottom of the sensor, whereby the metal plate ends flush with the lower side of the sensor or of the sensor housing and thus in functional use with the window.
The sensor can be glued onto the window by means of a thin film with a high thermal conductivity.
In a preferred embodiment, the sensor is integrated into a sensor module, thereby creating a small-scale sensor module, which preferably also contains evaluation electronics. The sensor module can be preferably integrated on or in a base of an interior mirror. The evaluation electronics of the module are protected by the sensor housing against external effects.
In a further embodiment, the capacitative operating moisture sensor, for example, consists of two electrodes, with a moisture-sensitive polymer element between them. The direct thermal coupling occurs preferably via one of the electrodes. Alternatively, the metal plate can be used, which is thermally connected to one of the electrodes.
The sensor need not necessarily be made with a polymer film. All other types of moisture sensing elements or sensors can also be used, e.g., with an interdigital structure, resistive elements, etc.
In an improvement, the sensor and evaluation electronics are placed in a small common housing.
In a further embodiment, the window temperature can be measured with use of a temperature sensor, which is preferably also integrated into the module, if a relative humidity in the vehicle interior is to be determined with this sensor module. The relative humidity can then be obtained from the determined window moisture, window temperature, and temperature in the passenger compartment. An additional interior moisture sensor is not necessary. Nonetheless, in this indirect humidity determination, the actual moisture in the passenger compartment is also determined as a function of influencing variables in the passenger compartment, such as the number and temperature of the passengers themselves.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.